Rotatable weld cutting tool

ABSTRACT

Apparatus is disclosed for detaching seal-welded heater elements from assembly with the pressurizer of a pressurized water nuclear power system. The heater elements are of the type that are connected to the pressurizer by both a seal weld and a mechanical back-up connection. The disclosed arrangement involves the use of the nut that forms part of the back-up connection as means for connecting a rotary weld cutter to its drive motor. A weld cutter of particular design capable of removing the seal weld without damaging the heater element is also described.

United States Patent 1 Penfield, Jr. et a1.

1 1 May 8,1973

[54] ROTATABLE WELD CUTTING TOOL [75] Inventors: Scott R. Penfield, Jr.,Warren W. Roberts, both of Chattanooga, Tenn.

[73] Assignee: Combustion Engineering Inc.,

Windsor, Conn.

[22] Filed: Nov. 18, 1970 [21] Appl. No.: 90,510

[52] US. Cl. ..30/124, 30/97, 30/276 [51] Int. Cl. ..B25f 3/00, B26b1/00, B26b 3/00 [58] Field of Search ..30/124, 96, 95, 97,

[56] References Cited UNITED STATES PATENTS Borden ..30/95 Studebaker etal ..30/97 FOREIGN PATENTS OR APPLICATIONS 715,297 8/1965 Canada 30/300940,975 3/1956 Germany ..30/95 Primary Examiner-James L. Jones, Jr.

Attorney-Carlton F. Bryant, Eldon H. Luther, Robert L. Olson, John F.Carney, Richard H. Berneike, Ed-

ward L. Kochey, Jr. and Lawrence P. Kessler [57] ABSTRACT Apparatus isdisclosed for detaching seal-welded V heater elements from assembly withthe pressurizer of a pressurized water nuclear power system. The heaterelements are of the type that are connected to the pressurizer by both aseal weld and a mechanical back-up connection. The disclosed arrangementinvolves the use of the nut that forms part of the backup connection asmeans for connecting a rotary weld cutter to its drive motor. A weldcutter of particular design capable of removing the seal weld withoutdamaging the heater element is also described.

7 Claims, 13 Drawing Figures PATENTED HAY 81975 SHEET 1 IF 4 INVENTOR.SCOTT 1?.PENF/ELD J2.

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ATTORNEY PATENTEU HAY 73 SHEET 3 0F 4 m -Ql INVENTOR scorr e. PEA/FIELDJ2. WARREN W-RO5E2T5 A RNEY i l, EMF Ell ROTATABLE WELD CUTTING TOOLBACKGROUND OF THE INVENTION Nuclear vapor generating plants of thepressurized water type include pressurizers which serve principally tomaintain the fluid pressure of the primary coolant system withinpredetermined limits during various stages of system operation.Pressurizers commonly employed in such systems comprise pressure vesselscontaining a body of saturated liquid into which a plurality of heaterelements are caused to extend. The heater elements are operated to addheat to the liquid in order to adjustably maintain a vapor head withinthe vessel and thereby regulate the fluid pressure of the primarycoolant system.

Heater elements of the disclosed type are electrically operated andextend through sleeves that penetrate the lower closure head of thevessel into the interior thereof. The elements adjacent their exposedends are seal welded to the sleeves to prevent leakage of liquid fromthe vessel interior. A mechanical back-up connection in the form of athreaded nut and bushing arrangement is also provided. Its purpose is toprevent axial retrograde movement of the heater element in the event offailure of the weld, which movement could cause considerable damage dueto the high fluid pressure present within the pressure vessel.

It occasionally happens that heater elements malfunction and must berepaired or replaced. Moreover, pressure boundary welds such as thosebetween pressurizer heater sleeves and the pressurizer shell cladrequire periodic inspection which requires the removal of an operativeheater element. In the past, removal of a heater element for any of theforegoing reasons required either destruction of the element caused bysevering it and its protective sleeve adjacent the seal weld orprolonged exposure of personnel to a highly radioactive environment whenthe element was removed intact by manual grinding of the seal weld. Bothof these forms of heater element removal are undesireable.

It is to the alleviation of this problem that the present invention isdirected.

SUMMARY OF THE INVENTION According to the present invention means areprovided for removing the welded connection between a heater element andits protective sleeve in a pressurizer assembly. The weld is removed insuch a manner as will prevent damage to either the heater element or thesleeve such that their reuse will be permitted. A weld cutting tool isarranged with radially extending cutter bits and is adapted to berotatably driven in order to remove the weld by means of acircumferential cut. The body of the cutting tool is split to permit itsengagement with the annular weld about the heater element and thesleeve. The tool is operated by a rotary drive motor and connection ofthe tool to the motor is effected by means of a drive collar arranged toengage the nut member of the back-up connection which, in turn, servesto maintain the tool body in assembled relation as well as to connect itto the collar.

By means of the invention more effective use of pressurizer heaterelements is permitted by virtue of the fact that, in the event of a needfor tool removal, the heater elements can be removed intact from theassembly and thereafter reassembled thereto for reuse.

DESCRIPTION OF THE DRAWINGS FIG. I is a schematic representation of atypical nuclear vapor supply of the pressurized water type;

FIG. 2 is a sectional elevation of a pressurizer heater elementassembly;

FIG. 3 is a sectional elevation of the apparatus of the presentinvention assembled in operative relation to the heater element of FIG.2;

FIG. 4 is an exploded view of the cutting tool of the present invention;

F IG. 5 is a view taken along line 55 of FIG. 4;

FIG. 6 is a view taken along line 6-6 of FIG. 4;

FIG. 7 is an elevational view of a drive collar according to the presentinvention;

FIG. 8 is a view taken along line 8-8 of FIG. 7;

FIG. 9 is a view taken along line 9--9 of FIG. 7; and

FIGS. 10-13 are views illustrating the various steps employed inremoving a heater element seal weld according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION Referring toFIG. 1 there is shown a schematic representation of nuclear vapor supplysystem 10 that is typical of those of the pressurized water type. Itcomprises a neutronic reactor 12 having a primary coolant systemincluding lines 14 and 16 for circulating a primary coolant, such aspressurized light water, between the reactor and a vapor generator 18 inwhich a second liquid is vaporized for subsequent use in a prime mover(not shown). The primary coolant system includes a pressurizer 20 thatcommunicates with the line 14 and operates to maintain the fluidpressure in the system within predetermined limits during various stagesof system operation.

As is well known, the pressurizer 20 comprises a closed vesselcontaining a body of liquid that forms part of the primary coolantcirculated through the system. The coolant contained within the vesselwhich is maintained at saturated temperature, immerses the operatingends of a plurality of electrical heating elements 22. The heatingelements 22 are arranged to controllably add heat to the enclosed liquidthereby to adjustably maintain a vapor head within the vessel thatregulates the fluid pressure of the primary coolant system.

In FIG. 2 there is illustrated in greater detail the assembledconnection of a heater element 22 to the pressurizer vessel 20. Asshown, the heater element 22 includes an elongated cylindrical shaft 24adapted to extend upwardly through the bottom end of the vessel. At itsexternal end shaft 24 is provided with an enlarged head 26 that servesto connect the element 22 with a source of electrical power. Theassembly includes a sleeve 28 attached within a bore in the lower vesselclosure. The sleeve is welded at its inner end to the cladded interiorsurface 30 thereof. The shaft 24 of the heater element extends throughthe sleeve 28 and is welded thereto at the exterior end thereof as at 32in order to effect a fluid-tight seal between the heater element and thesleeve.

The assembly also includes a mechanical back-up connection, indicatedgenerally as 34, that serves to protect against retrograde movement ofthe heater element from the sleeve in the event of rupture or failure ofthe seal weld 32. This connection comprises an anment shaft 24. When thenut 38 is threaded to the bushing 36 the stop ring 42 abuts the shoulder40 thereby preventing the heater element 22 from being propelled fromthe sleeve under the influence of high fluid pressure existing withinthe vessel in the event of failure of the weld 32.

According to the present invention means are provided for removing theseal weld 32 between the heater element 22 and sleeve 28 in a manner aswill prevent damage to these two pressurizer components thus to enabletheir reuse. The manner contemplated includes a rotary cutting tool 44that is adapted for operation by a drive motor 46. The connectionbetween the tool 44 and drive motor 46 is effected by means of a drivecollar 48 that is adapted to drivingly attach the hollow nut 38 whichforms part of the mechanical back-up connection and which, in turn, isarranged to connect the cutting tool 44.

The cutting tool 44 according to the invention is shown in detail inFIGS. 4, and 6 of the drawing. The tool body 50 comprises a pair of bodysegments 50a and 50b which, when assembled, define an annular memberhaving a central opening 56 that receives the shaft 24 and into which aplurality, here shown as being three in number, of radially extendingweld cutting bits 58 extend. The cutting bits 58 are rectangular insection and are retained in the tool body 50 within cylindrical sleeves60 that are pressed into circumferentially spaced radial bores throughthe body. The sleeves 60 each contain a central bore, the forwardportion 62 of which is of rectangular cross section to receive therespective bits 58 and the rearward portion 64 of which contains aninternal thread for reception of set screws 66. The set screws 66 serveto enable radial adjustment of the bits with respect to the axis of thetool in order that the tool can operate on welds of varying diameters.Other set screws 68 are disposed normally to the axis of the respectivebits and serve to lock the bits in their adjusted position within thetool body.

The element indicated as 59 has essentially the same structure as thecutting bits 58 except to the extent that instead of being provided witha cutting head the element is formed with a bronze bearing surface. Thiselement, like the cutting bits 58, is radially adjustable, by means ofset screw 66 and serves to set the effective radial distance between theaxis of the tool and the cutting bits.

The outer periphery of the body halves, 50a and 50b, are each providedwith a plurality of spaced rectangular grooves 70 adapted to connect thedrive collar 48 as herein after described. Each groove 70 extendslongitudinally of the body halves and contains chamfered edges 72 alongone side to facilitate reception of the drive collar.

The tool body 60 is preferably provided with an arcuate bearing surface74, here shown on body half 50b and interrupted by an opening 76 for oneof the cutting bits 58. This surface is placed in substantial alignmentwith the location of the cutting bits 58 and functions primarily tocenter the cutting tool body 50 about the heater element shaft 24 priorto operation of apparatus.

The tool body half 50b is provided with oppositely spaced radial flanges78 containing through-openings for reception of the cap screws 52, thethreaded ends of which are connected in threaded bores 80 provided inbody half 50a. Assembly of the two body halves 50a and 50b isfacilitatedby centering pins 54 which, in the disclosed arrangement, have one endpressed oppositely spaced into bores provided on the facing surface ofbody half 50a. The other body half 50b contains bores 82 of slightlygreater diameter for sliding reception of the other ends of thecentering pins 54.

As best shown in FIG. 5 the tool body halves 50a and 50b are providedwith axial extentions 84 that define an axially elongated cylinderformed with an external thread 86. According to the invention thisthread 86 conforms with that on the bushing 36 that forms part of themechanical back-up connection thereby enabling use of the hollow nut 38of that assembly as the connector member for mounting the segments 50aand 50b of the tool body.

FIGS. 7, 8 and 9 illustrate in detail the drive collar 48 according tothe present invention. This component of the apparatus cooperates withthe hollow nut 38 to establish connection between the cutting tool 44and drive motor 46. The collar 48 has an axially elongated, hollowcylindrical body 88 whose interior is sized to extend over the exposedend of the heater element 22 as shown in FIG. 13. The rearward end ofthe body 88 is closed by an end plate 90 that axially mounts a shaft 92for connection with a drive motor 46. As shown, the shaft 92 may containa plurality of circumferentially spaced, longitudinal flats 94 forengaging chuck elements associated with the drive motor. The leading endof the body 88 is open and provided with four circumferentially spacedlongitudinal protuberances 96 that are adapted to engage the respectivegrooves 70 in the cutting tool body 50.

Adjacent its leading end, the wall of the collar body 88 is providedwith a pair of diametrically opposed slots 98 which serve to lendflexibility in the body at this end. Flange pairs 100 are disposedadjacent the respective slots 98 with the flanges in each pair beingoppositely spaced from the associated slots and containing openings tomount bolt connectors 102. In this way a relatively tight engagement canbe established between the drive collar 48 and the hollow nut 38 uponassembly of the apparatus thereby to reduce the vibration or chatterthat could occur between these members during the cutting operation.

The collar body 88 further includes a pair of limit pins 104 providedwithin the interior thereof. The pins 104 are preferably located atdiametrically opposite positions with each being welded or otherwisesecured to the interior surface of the body and extending radiallytherefrom a distance sufficient to enable the pins to engage the rearend of the nut 38. The pins 104 are so disposed to prevent retrogrademovement of the nut 38 within the interior of the collar body 88. Byrestricting the location of the nut to closely-adjacent the leading endof the drive collar, connection of the nut to the segments of the toolbody 50 is greatly facilitated.

The interior of the drive collar is further provided with an annularbushing 106 that is suitably secured, as by means of threadedconnectors, to the inner surface of the body collar 88. The bushing 106contains a central bore 108 having a tapered surface opening toward theopen end of the collar thereby to enhance sliding reception of thebushing upon the enlarged head 26 of the heater element 22 when thedrive collar is extended over the latter. The minor diameter of the bore1618 is sized such that the bushing can slidingly engage the head 28thereby serving to center the apparatus upon the heater element 22during operation of the cutting tool.

The operation of the invention is described with particular reference toFIGS. -13 which disclose the apparatus in various stages of assembly.Beginning with a pressurizer heater element assembly as shown in FIG. 2,the mode of utilizing the present invention is begun, as shown in FIG.10, by unthreading the hollow nut 38 from the bushing 36 of themechanical back-up connection and moving the former axially along theheater element shaft 24 so as to expose the seal weld 32 to be removed.Next, the segments of the body 50 of the cutting tool 44 are assembledupon the shaft 24 closely adjacent the weld 32. After the cap screws 52have been tightened to engage the body segments about the heater elementshaft the hollow nut 38 is moved along the shaft and threadedlyconnected about the external 7 thread 86 on the axial edge 84 of thebody 50 as shown in FIG. 12. With the set screws 68 loose (FIG. 4), setscrews 66 are manipulated to move the respective cutting bits 58 intoconcentric engagement with the weld 32. Thereafter, the drive collar 48is axially extended over the assembly with the protuberances 96 placedin engagement in the drive grooves 70 in the tool body 50. Bolts 102 aretightened to ensure a snug fit between the collar 48 and the nut andtool assembly. Threaded connector 110, as shown in FIG. 13, mayadditionally be employed to positively lock the drive collar 48 to thenut 38. Rotary movement of the cutting tool 44 is effected by attachingthe drive motor 46 to the shaft 92 of the drive collar. The apparatus ismanually manipulated and the drive motor 46 operated until the seal weld32 has been removed thus to sever the connection. Metal chips and anysmall amount of leakage liquid that may have been disposed behind theseal are discharged into the interior of the drive collar 48 thus toprotect the workman operating the tool.

It will be appreciated that once the seal weld 32 has been removed theheater element 22 can be simply slidingly removed, still intact, fromthe p'ressurizer sleeve 28. The desired maintenance, repair orinspection can then be performed and thereafter the heater elementreturned to its operative position within the sleeve 28 to be reused.

The present invention therefore provides a simple and inexpensive meansfor quickly removing heater elements from assembly in a pressure vesselin a manner as will maintain the heater element intact. In this way, aninoperative heater element can simply be repaired and thereafterreturned to service. This is in contradistinction to prior artarrangements which require complete severence of the heater element inorder to remove it from the assembly within the pressurizer therebycompelling its replacement which results in a considerably moreexpensive operation of the pressurizer.

It will be understood that various changes in the details, materials,and arrangement of parts which have been herein described andillustrated in order to explain the nature of the invention may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the claims.

What is claimed is:

1. For use in a pressurizer organization including a substantiallyclosed vessel, a sleeve attached at its lead ing end to a bore in saidvessel, a heater element, cylindrical in section and longer than saidsleeve extending into said vessel in sheathed relation within saidsleeve, and a seal weld between said sleeve and said heater elementadjacent and exposed ends thereof, apparatus for removing said seal weldcomprising:

a. a rotatable weld cutting tool including a body having a centralopening for reception upon said heater element and radially adjustablecutting bits extending into said opening and engageable with said sealweld;

. means for rotatably driving said weld cutting tool;

and

. means for connecting said weld cutting tool to said tool-driving meansincluding an elongated, hollow cylindrical body member concentricallydisposed about the exposed end of said heater element, means on saidbody member for radially engaging the body of said cutting tool andother means axially spaced from said tool-engaging means for attachingsaid body member to said tool-driving means.

2. Apparatus as recited in claim 1 wherein the body of said cutting toolcontains a plurality of circumferentially spaced, longitudinallyextending grooves about the outer periphery thereof and said body memberincluded protuberances extending from the leading end thereof adaptedfor engagement with said grooves.

33. Apparatus as recited in claim 2 wherein the body of said cuttingtool is diametrically split to define a pair of body segments and meansfor detachably joining said body segments about said heater element.

4. For use in a pressurizer organization including a substantiallyclosed vessel, a sleeve attached at its leading end to a bore in saidvessel, a cylindrical heater element having an elongated shaft and anenlarged head at one end thereof, said shaft being longer than saidsleeve and extending into said vessel in sheathed relation within saidsleeve, a seal weld between said sleeve and said heater element shaftadjacent the exposed end thereof and a mechanical back-up connectionincluding a nut member concentrically slidably mounted on said heaterelement shaft for threaded connection to said sleeve, apparatus forremoving said seal weld comprising:

a. a rotatable weld cutting tool including:

i. a plurality of segments arranged to define a cutter body having acentral opening for reception upon the shaft of said heater element,said segments including means defining an externally threaded axialappendage for reception of said nut member for detachable assembly ofsaid segments;

ii. a plurality of radial bores extending through said body segments,

iii. cutting bits adjustably mounted in said radial bores and extendinginto said central opening for engagement with said seal weld;

b. motor drive means for rotating said weld cutting tool; and

c. means for connecting said weld cutting tool to said motor drivemeans.

5. Apparatus as recited in claim 4 wherein the means for connecting theweld cutting tool to said motor drive means comprises:

a. an elongated, hollow cylindrical body member having an open'leadingend for concentric disposition over the exposed heater element head andshaft portion,

b. means on said body member for radially engaging the body of saidcutting tool, and

c. means axially spaced from said tool-engaging means for attaching saidbody member to said tool-driving means.

6. Apparatus as recited in claim 5 wherein said body member is closed atits rearward end to define a substantially closed receptacle whenassembled to said cutting tool body.

7. Apparatus as recited in claim 5 wherein said nut body segments areprovided with circumferentially spaced, longitudinally extending groovesabout their outer periphery and the body member of said connecting meansincludes a plurality of circumferentially spaced, longitudinallyextending protuberances about its leading end for reception in saidgrooves.

1. For use in a pressurizer organization including a substantiallyclosed vessel, a sleeve attached at its leading end to a bore in saidvessel, a heater element, cylindrical in section and longer than saidsleeve extending into said vessel in sheathed relation within saidsleeve, and a seal weld between said sleeve and said heater elementadjacent and exposed ends thereof, apparatus for removing said seal weldcomprising: a. a rotatable weld cutting tool including a body having acentral opening for reception upon said heater element and radiallyadjustable cutting bits extending into said opening and engageable withsaid seal weld; b. means for rotatably driving said weld cutting tool;and c. means for connecting said weld cutting tool to said tooldrivingmeans including an elongated, hollow cylindrical body memberconcentrically disposed about the exposed end of said heater element,means on said body member for radially engaging the body of said cuttingtool and other means axially spaced from said tool-engaging means forattaching said body member to said tool-driving means.
 2. Apparatus asrecited in claim 1 wherein the body of said cutting tool contains aplurality of circumferentially spaced, longitudinally extending groovesabout the outer periphery thereof and said body member includedprotuberances extending from the leading end thereof adapted forengagement with said grooves.
 3. Apparatus as recited in claim 2 whereinthe body of said cutting tool is diametrically split to define a pair ofbody segments and means for detachably joining said body segments aboutsaid heater element.
 4. For use in a pressurizer organization includinga substantially closed vessel, a sleeve attached at its leading end to abore in said vessel, a cylindrical heater element having an elongatedshaft and an enlarged head at one end thereof, said shaft being longerthan said sleeve and extending into said vessel in sheathed relationwithin said sleeve, a seal weld between said sleeve and said heaterelement shaft adjacent the exposed end thereof and a mechanical back-upconnection including a nut member concentrically slidably mounted onsaid heater element shaft for threaded connection to said sleeve,apparatus for removing said seal weld comprising: a. a rotatable weldcutting tool including: i. a plurality of segments arranged to define acutter body having a central opening for reception upon the shaft ofsaid heater element, said segments including means defining anexternally threaded axial appendage for reception of said nut member fordetachable assembly of said segments; ii. a plurality of radial boresextending through said body segments, iii. cutting bits adjustablymounted in said radial bores and extending into said central opening forengagement with said seal weld; b. motor drive means for rotating saidweld cutting tool; and c. means for connecting said weld cutting tool tosaid motor drive means.
 5. Apparatus as recited in claim 4 wherein themeans for connecting the weld cutting tool to said motor drive meanscomprises: a. an elongated, hollow cylindrical body member having anopen leading end for concentric disposition over the exposed heaterelement head and shaft portion, b. means on said body member forradially engaging the body of said cutting tool, and c. means axiallyspaced from said tool-engaging means for attaching said body member tosaid tool-driving means.
 6. Apparatus as recited in claim 5 wherein saidbody member is closed at its rearward end to define a substantiallyclosed receptacle when assembled to said cutting tool body.
 7. Apparatusas recited in claim 5 wherein said nut body segments are provided withcircumferentially spaced, longitudinally extending grooves about theirouter periphery and the body member of said connecting means includes aplurality of circumferentially spaced, longitudinally extendingprotuberances about its leading end for reception in said grooves.